Abstract

We perform third-harmonic (TH) spectroscopy on rod-type gold nanoantenna arrays using widely tunable sub-30 fs laser pulses. We find the peak of the TH generation efficiency of the antenna arrays always slightly redshifted with respect to the peak of their linear extinction spectrum. We model the wavelength-dependent TH response quantitatively using a nonlinear harmonic oscillator model.

Top: Measured Gaussian laser spectra, which are used for the TH spectroscopy experiments. The laser spectrum is shifted in steps of 20 nm over the linear antenna resonance (black) and at each spectral position a TH is generated. Bottom: Measured normalized TH spectra. For clarity only every second laser and TH spectrum is depicted.

Measured and modeled normalized TH efficiencies with respect to their linear extinction spectra. From top to bottom the length of the antennas increases from 200 to 245 nm. The insets show colored SEM images of a single antenna of the corresponding antenna array.